The present invention relates to track offset calibration of an optical storage device, and more particularly, to systems and methods for calibrating a recording track offset of an optical storage device accessing an optical storage medium of a land and groove recording/reproduction type.
Regarding a digital versatile disc (DVD) such as a DVD-Recordable (DVD-R) disc, accurately controlling a track offset of an optical head of a DVD drive during recoding data onto the DVD-R disc is not so important to the recording quality thereof since no obvious problem would occur even if the laser light spot emitted from the optical head is not locked at the center of a groove track of the DVD-R disc. However, regarding a DVD-RAM disc, if the laser light spot emitted from the optical head is not locked at the center of a second track of the DVD-RAM disc while the DVD drive is recording data on the second track, data previously written on a first track adjacent to the second track would probably be erased or overwritten, typically causing a large jitter value that represents poor recording quality. In the worst case, at least a portion of the data on the DVD-RAM disc becomes unreadable.
For example, the second track is a groove track 21G centered at line (b) as shown in FIG. 1, where address blocks 16 to 19 are indicated as ID1 to ID4, respectively. If the laser light spot 24 scans along line (a) while the DVD drive is recording data on the groove track 21G, the data previously written on the first track, which is the land track 21L adjacent to the groove track 21G in this situation, would be damaged. If the laser light spot 24 scans along line (c) while the DVD drive is recording data on the groove track 21G, the data previously written on the first track, which is the land track 22L adjacent to the groove track 21G in this situation, would be damaged.
Sometimes, a typical value of the recording track offset (the track offset in a recording process) would be different from a typical value of the reading track offset (the track offset in a reading process) due to luminosity variations of the laser light spot and unbalance of a so-called PDIC gain. According to the related art, performing online closed loop control would probably be helpful on controlling the recording track offset, where an all sum (AS) signal corresponding to a radio frequency (RF) signal can be utilized for controlling the laser light spot 24 to scan along line (b), as shown in FIG. 2.
During an optimal power calibration (OPC) process that is typically performed before a recording process, if an initial value of the recording track offset (e.g., a zero initial value) is inappropriate, which means the initial value of the recording track offset is far from a real value corresponding to a real radial location of the optical head with respect to a track, an OPC fail would probably occur. Even if no OPC fail occurs, a calibrated value of the recording power of the optical head is usually higher than a typical value of the recording power, which leads to problems such as a decreasing number of overall rewritable times of the DVD-RAM disc, a higher error rate, and a greater jitter value.
Regarding a recording process without performing the OPC process in advance, if an initial value of the recording track offset is unsuitable, first recorded data (e.g. the data previously recorded on the first track mentioned above) will be partially/fully erased or overwritten by later recorded data (e.g. the data recorded on the second track mentioned above). As a result, at least a portion of the first recorded data on the DVD-RAM disc is lost.